Need some good advice on the best way to set the back edge of a small roof (patio shelter) on a 2nd story deck about one third of the way up the slope of the house roof. Primary goal is to not create a potential leak for the house and to not interrupt the gutter flow. Thanks.

If you want to do it correctly...remove shingles and install flashing as needed.
Another way is to install some 3 inch plumbers roof vents and use pipe to attach your structure to in the attic. Then flash it or use rubber roofing. We have used this to build a deck over a roof.
Without seeing a picture or having a little more to work with....thats all I have.

Is there already a roof over the deck? I'm assuming not, since if there was it would already be attached. The proper method is to cut back the shingles and build the deck roof against the roof sheething. Flash the valeys and shingle the roof as normal.

If possible, maybe you could attach a photo of what you're talking about and I could go into more detail.

Appreciate the good ideas. House roof is a 3/12 hip and the it's a simple one plane slope in the back. Patio roof would be a pergola style, flat roof. I like the idea of setting a support on metal brackets so that water could flow under. Is there such a thing available (angled flat plate on the bottom, u-shaped bracket on top). Would it be better to fasten a plate on top of the sheathing and then replace flashing and shingles or go through the sheathing and attach to rafters? Thanks again.